US10005063B2

US10005063B2 - Method of adsorbing iodine or bromine

Info

Publication number: US10005063B2
Application number: US14/646,952
Authority: US
Inventors: Kyung Byung Yoon; Cao Than Tung Pham; Yong Su Park
Original assignee: Sogang University Research Foundation
Current assignee: Sogang University Research Foundation
Priority date: 2012-11-23
Filing date: 2013-11-25
Publication date: 2018-06-26
Also published as: CN104936691B; EP2923755A1; WO2014081259A1; EP2923755A4; EP2923755B1; US20160038912A1; KR20140066933A; CN104936691A; KR102035867B1; JP2016505360A

Abstract

The present invention relates to an iodine (I₂) or bromine (Br₂) adsorbent including a zeolite having a Si/Al ratio of 15 or greater; an I₂or Br₂carrier including the I₂or Br₂adsorbent; a column filled with the I₂or Br₂adsorbent; a article composed of the I₂or Br₂adsorbent or having the I₂or Br₂adsorbent attached thereto; a method for adsorbing or removing I₂or Br₂using the I₂or Br₂adsorbent; an iodine- or bromine-containing zeolite composite including a porous zeolite and iodine (I₂) or bromine (Br₂) confined in the pores of the zeolite; a semiconductor material including the iodine- or bromine-containing zeolite composite; and a method for preparing an iodine- or bromine-containing product using the iodine- or bromine-containing zeolite composite.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage of International Application No. PCT/KR2013/010735, filed on 25 Nov. 2013 claiming the priority of KR 10-2012-0134078 filed on 23 Nov. 2012, the content of each of which is incorporated by reference herein.

BACKGROUND

1. Field

2. Description of the Related Art

Iodine is a volatile (sublimating), corrosive solid at room temperature. Because of its volatility, it is difficult to accurately weigh the amount of iodine on a scale, and iodine vapor can corrode the scale being used. Likewise, bromine, being a highly volatile and corrosive liquid at room temperature, is difficult to accurately weigh on a scale, and bromine vapor can corrode the scale being used.

Of the 37 known isotopes of iodine, all are radioactive elements except the stable I-127. Whereas most of the radioactive isotopes have very short half-lives of 1 day or shorter, I-124, I-125, I-126, and I-131 have relatively long half-lives of 4-60 days. Among them, I-131 results in the greatest radioactive damage in the event of atomic reactor explosion. I-129 decays over a very long period of time with a half-life of Ser. No. 15/700,000 years. Due to its slow radioactive radiation, it is less dangerous than other radioactive isotopes and is classified as a potential radioactive material since a large amount of radioisotopes, despite slow radioactive radiation, can lead to high radiation doses. However, the capture of this isotope is an important part in the process of nuclear waste because about 0.55% of uranium decays into I-129. Since I-129 exists naturally at a certain level, it can be used as an index for chronometry. That is to say, the trace amount of the naturally existing I-129 captured enables accurate timekeeping.

In solutions, iodine usually exists as iodide ions (I⁻) and iodine molecules (I₂). Theoretically, the iodide anions can be recovered using an anion exchanger. However, once the ions flow into seawater, it is impossible to recover the iodide ions using the anion exchanger because of the high chloride concentration in seawater. The neutral iodine molecules are oxidative and are easily converted into iodide ions via oxidation by various reducing materials present in seawater. Therefore, the neutral iodine molecules need to be recovered from the hydrosphere including the sea or air before they are converted into iodide ions. For this reason, a method allowing for effective capturing of iodine included in water or air may be useful for blocking the propagation of the radioactive iodine.

Until recently, activated carbon or zeolite has been used to recover neutral iodine molecules from water or air. However, these adsorbents tend to reduce a significant amount of the adsorbed neutral iodine to iodide ions. Due to this property, it is difficult to remove iodine, particularly that in water. Therefore, it is necessary to develop an iodine adsorbent or capturing agent capable of capturing neutral iodine well without converting the neutral iodine molecules to iodide ions.

SUMMARY

Activated carbon (AC) is known to adsorb I₂well. However, a considerable amount of the adsorbed I₂is reduced to I⁻ by reducing materials present in the activated carbon. It is difficult to remove the thus generated I⁻, and the I₂-adsorbing ability of the activated carbon containing I⁻ is very low. Accordingly, when removing I₂from waste fuel using AC filled into a fixed bed, the AC in the fixed bed should be replaced with fresh AC after several charge-discharge cycles. Accordingly, there is a need for a strong physical adsorbent enabling purely physical adsorption even after many charge-discharge cycles without the need for replacement.

The present inventors have examined various zeolites for their I₂-adsorbing ability and formation of I⁻ following I₂adsorption. As a result, the inventors have found that a zeolite having a high Si/Al ratio adsorbs well not only iodine gas (I₂) in the air but also I₂dissolved in water, and the adsorbed I₂can be separated as I₂because it is not reduced to I⁻. As a result, the zeolite adsorbent can be recycled many times with no decline in adsorbing ability. Also, the inventors have found that the zeolite can adsorb not only I₂but also Br₂as well. In addition, the inventors have found that the iodine (I₂) confined in the pores of the zeolite can be readily desorbed using an organic solvent and completely desorbed by heating.

Furthermore, the inventors have found that the iodine- or bromine-containing zeolite composite exhibits semiconductor properties and, accordingly, zeolites in which iodine molecules or bromine molecules are included can be used for various applications.

The present invention is based on these findings.

In an aspect, the present invention provides an I₂or Br₂adsorbent containing a zeolite having a Si/Al ratio of 15 or greater.

Specifically, the zeolite may have a Sanderson partial negative charge on oxygen (−δ₀) of 0.2 or lower.

Non-limiting examples of the zeolite may include SL-1F, Si-BEA, SL-1, ZSM-5, MTW, silica MTW, silica DDR, high-silica DDR (ZSM-58, Si/Al=190), silica SSZ-73, an all-silica clathrasil DD3R, a silica ferrierite, silica TON, silica LTA, silica ITQ-1, silica ITQ-2, silica ITQ-3, silica ITQ-4, silica ITQ-7, silica ITQ-29, silica ITQ-32, a silica zeolite having CHA, STT, ITW or SVR topology, silica FAU, silica AST, a silica zeolite YNU-2 having MSE topology, silica RUB-41, silica ZSM-22, silica MEL, or a zeolite analogue having a Si/Al ratio of 15 or greater. Preferred examples of the zeolite may include silicalite-1 (SL-1), fluoride (F⁻)-added silicalite-1 (SL-1F) synthesized by adding a fluoride (F⁻)-releasing reagent, a beta zeolite having a silica backbone (all-silica beta, Si-BEA), TON having a silica backbone (ZSM-22), a ferrierite having a silica backbone (ZSM-35), DDR having a silica backbone, ZSM-5, etc., or a mixture thereof. In the iodine (I₂) or Br₂adsorbent according to the present invention, the zeolite may be in the form of powder, foam, or film or may be a blended mixture with a natural polymer, a synthetic polymer, or another zeolite not having superior iodine- or bromine-adsorbing ability.

In another aspect, the present invention provides an I₂or Br₂carrier including the I₂or Br₂adsorbent according to the present invention; a fixed-bed column filled with the I₂or Br₂adsorbent according to the present invention; and a article composed of the I₂or Br₂adsorbent according to the present invention or having the I₂or Br₂adsorbent attached thereto. The article may be clothing.

Non-limiting examples of methods for preparing a zeolite foam or attaching a zeolite onto a substrate are described in Korean Patent Nos. 0392408 and 0607013 owned by the inventors of the present invention, which are incorporated herein by reference.

In another aspect, the present invention provides a method for adsorbing I₂or Br₂, including adsorbing I₂or Br₂using the I₂or Br₂adsorbent according to the present invention, the fixed-bed column according to the present invention, or the article according to the present invention.

In another aspect, the present invention provides a method for removing I₂or Br₂, including: adsorbing I₂or Br₂using the I₂or Br₂adsorbent according to the present invention, the fixed-bed column according to the present invention, or the article according to the present invention; desorbing the adsorbed I₂or Br₂from the zeolite by bringing into contact with an organic solvent dissolving I₂or Br₂, by heating, or by blowing in heated air or nitrogen; and forming an insoluble silver iodide or silver bromide precipitate by reacting the desorbed I₂or Br₂with AgNO₃.

In another aspect, the present invention provides an iodine- or bromine-containing zeolite composite including a porous zeolite and iodine (I₂) or bromine (Br₂) confined in the pores of the zeolite. A known content of iodine or bromine may be captured in the composite.

The iodine- or bromine-containing zeolite composite according to the present invention exhibits semiconductor properties and, thus, can be used as a semiconductor material.

In another aspect, the present invention provides a method for preparing an iodine- or bromine-containing product or a compound generated by an iodine or bromine catalyst, including forming an iodine- or bromine-containing product in an organic solvent dissolving I₂or Br₂via a chemical reaction between iodine or bromine desorbed from the iodine- or bromine-containing zeolite composite according to the present invention by the organic solvent and another compound, or forming the compound in an organic solvent dissolving I₂or Br₂via a catalytic action of the iodine or bromine, desorbed from the iodine- or bromine-containing zeolite composite according to the present invention by the organic solvent. This is based on the point that the iodine- or bromine-containing zeolite composite confines iodine (I₂) or bromine (Br₂) in pores thereof and the I₂or Br₂may be released by an organic solvent, heat, or contact with hot air or nitrogen.

A zeolite having a Si/Al ratio of 15 or greater can adsorb not only iodine (I₂) or bromine (Br₂) gas in the air but also I₂or Br₂dissolved in water. In particular, it can adsorb and capture not only the radioactive iodine gas in the air but also the radioactive I₂or Br₂dissolved in seawater or underground water. Furthermore, among the zeolites according to the present invention, a zeolite having a Sanderson partial charge on oxygen (−δ⁰) of 0.2 or lower convert neither the adsorbed I₂to I⁻ nor the adsorbed Br₂to Br⁻, and can release I₂or Br₂perfectly without loss, by contact with an organic solvent or by heating and, thus, can be recycled indefinitely.

In addition, since the iodine- or bromine-containing zeolite composite according to the present invention, which includes a porous zeolite and iodine (I₂) or bromine (Br₂) confined in the pores of the zeolite, exhibits semiconductor properties, it may be used as a semiconductor material. Furthermore, since it captures iodine (I₂) or bromine (Br₂), it may be used for various applications, e.g., as an iodine or bromine carrier or an iodine- or bromine-releasing reagent which releases an exact amount of iodine or bromine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows absorption of I₂from its saturated aqueous solution onto activated carbon (AC) and various zeolites SL-1F, Si-BEA, SL-1, ZSM-5, AgMOR, SBA-15, NaY, MOR, NaX, NaA, and CaA as solid absorbents.

FIG. 2 shows the absorbed amount (wt %) of iodine (I₂) (the amount (g) of absorbed I₂per 100 g of zeolite) with time for activated carbon (AC) and various zeolites in aqueous solutions.

FIG. 3 shows sublimation of I₂from solid I₂, and its absorption into silicalite foam (SL-1 form) and silicalite powder (SL-1 powder).

FIG. 4 compares the hydrophobicity of activated carbon (AC) and various zeolites through water vapor adsorption isotherms at 313 K (40° C.).

FIG. 5 shows an apparatus for desorbing I₂by increasing temperature while injecting nitrogen gas.

FIG. 6 shows the degree of desorption of I₂from solid absorbents according to temperature.

FIG. 7 shows XRD patterns of MFI-type zeolite powder (freshly calcined), MFI-type zeolite with 0.1%, 1.0%, 6.9%, 22.3%, or 34.4% I₂adsorbed, and I₂-adsorbed MFI-type zeolite which has been recalcined (recalcination).

FIG. 8a and FIG. 8b respectively show the amount (wt %) of iodide ion (I⁻) formed inside a solid absorbent (8 a) and in a solution (8 b) by activated carbon (AC) and various zeolites with time. FIG. 8a shows the amount (wt %) of iodide ion (I⁻) formed inside the solid absorbent, FIG. 8b shows the amount (wt %) of iodide ion (I⁻) formed in an aqueous solution, and FIG. 8c shows the total amount of the formed iodide ion (I⁻).

FIG. 9 shows the relationship between the Sanderson partial charge on oxygen and the total amount (wt %) of iodide ion (I⁻) formed inside a solid absorbent and in a solution for activated carbon (AC) and various zeolites.

FIG. 10A shows the absorbed amount (wt %) of I₂by activated carbon (AC) and various zeolites from the I₂-saturated aqueous iodide (I⁻) solution with various concentrations of I⁻. FIG. 10B shows the absorbed amount (wt %) of I₂by activated carbon (AC) and various zeolites from the I₂-saturated seawater.

FIG. 11 shows scattering and reflection UV-Vis spectra of Br₂-adsorbed Si-BEA, ZSM-5, and SL-1 DML. It can be seen that the zeolites effectively adsorb Br₂.

DETAILED DESCRIPTION

The term zeolite collectively refers to crystalline aluminosilicates.

The zeolite backbone is composed of tetrahedral units formed by [SiO₄]⁴⁻ and [AlO₄]⁵⁻, which are bridged by oxygen atoms. Since the Al of [AlO₄]⁵⁻ has a formal charge of +3, whereas the Si of [SiO₄]⁴⁻ has a formal charge of +4, each Al has one negative charge. Accordingly, cations are present for charge balancing. The cations are present not in the backbone but in the pores and the remaining space is usually occupied by water molecules.

Because the site occupied by aluminum in the aluminosilicate backbone is negatively charged, there are cations for charge balancing in the pores and the inside of the pores is strongly polarized.

Meanwhile, various analogues (zeotype molecular sieves), wherein the silicon (Si) and aluminum (Al) constituting the backbone structure of zeolite have been partially or entirely replaced by various other elements, are known. For example, a porous silicalite in which aluminum has been completely eliminated, an (AlPO₄)-type zeolite analogue in which silicon has been replaced by phosphorus (P), and other zeolite analogues obtained by replacing the backbone metal atoms of a zeolite or a zeolite analogue with various metal elements such as Ti, Mn, Co, Fe, Zn, etc. are known. These analogues are also included in the scope of zeolite according to the present invention.

Examples of an MFI-type zeolite or an analogue thereof may include ZSM-5, silicalite-1, TS-1, AZ-1, Bor-C, boralite C, encilite, FZ-1, LZ-105, monoclinic H-ZSM-5, mutinaite, NU-4, NU-5, TSZ, TSZ-III, TZ-01, USC-4, USI-108, ZBH, ZKQ-1B, etc. ZSM-5 is an MFI-type zeolite formed of silicon and aluminum of a specific ratio, silicalite-1 is a zeolite consisting only of silica (SiO₂), and TS-1 is an MFI-type zeolite in which titanium (Ti) occupies some of the aluminum sites.

Both SL-1 and SL-1F are MFI-type. SL-1 is synthesized without adding NH₄F at all, whereas SL-1F is synthesized by adding NH₄F to significantly increase hydrophobicity.

The chemical composition and the Sanderson partial charge on oxygen of various zeolites are given in Table 1.

	TABLE 1

	Chemical composition (formula)	−δ₀

SL-1	Si₉₆O₁₉₂	0.1501
Ag-MOR	H_4.0Ag_1.2Al_5.2Si_42.8O₉₆	0.1596
MOR	H_4.0Na_1.2Al_5.2Si_42.8O₉₆	0.1613
ZSM-5	H_0.2Na_0.75K_2.75Al_3.7Si_94.3O₁₉₂	0.1684
CaA	H₁₅Ca_22.5Na_34.5Al_94.5Si_97.5O₃₈₄	0.2615
NaY	Na_52.3Al_52.3Si_139.7O₃₈₄	0.2640
NaA	H₆Na_88.5Al_94.5Si_97.5O₃₈₄	0.3251
NaX	H₃Na_92.7Al_95.75Si_96.25O₃₈₄	0.3367

When I⁻ is generated in an I₂adsorbent, the I₂adsorbent can no longer adsorb I₂and the I⁻ is difficult to remove therefrom. When the I⁻ exists in a solution, it can be removed using an anion exchange resin or a silver solution. However, when the I⁻ exists inside the adsorbent, it cannot be removed even with the anion exchange resin or silver solution. The inventors of the present invention have examined various zeolites for their I₂-adsorbing ability and formation of I⁻ following I₂adsorption. As a result, the inventors have found that there are some zeolites which do not generate or hardly generate I⁻ after I₂adsorption, particularly in water.

A more detailed description is given herein below.

The I₂concentration of a saturated I₂aqueous solution is ˜1.5 mM. It was investigated whether activated carbon (AC) and various zeolites ZSM-5, SL-1 powder, SL-1 foam, Si-BEA, NaA, NaY, SBA-15, MOR, and AgMOR adsorb the I₂saturated in water well (FIG. 1). As seen from FIG. 1, activated carbon, zeolite ZSM-5, SL-1 powder, SL-1 foam, and Si-BEA can adsorb I₂in water.

Meanwhile, the adsorption amount (wt %) of iodine (I₂) with time for activated carbon (AC) and various zeolites SL-1F, Si-BEA (all-silica zeolite-β), SL-1, ZSM-5, AgMOR, SBA-15, NaY, MOR, NaX, NaA, and CaA was measured in aqueous solutions. As seen from FIG. 2, activated carbon and zeolite SL-1F, BEA, SL-1, and ZSM-5 showed high iodine (I₂) adsorption amount of 15 wt % or greater, whereas AgMOR, SBA-15, NaY, MOR, NaX, NaA, and CaA hardly adsorbed iodine (I₂).

In addition, the adsorption of I₂sublimating from solid I₂was confirmed for both silicalite-1 foam (SL form) and silicalite-1 powder (SL powder) which are MFI-type zeolites (FIG. 3). From FIG. 3, it can be seen that the color of the silicalite-1 foam and silicalite-1 powder turns violet due to the adsorption of I₂.

Meanwhile, the hydrophobicity of activated carbon (AC) and various zeolites SL-1F, Si-BEA, SL-1, ZSM-5, AgMOR, SBA-15, NaY, MOR, NaX, NaA, and CaA was investigated through water vapor adsorption isotherms at 313 K (40° C.). As seen from FIG. 4, the zeolites SL-1F, Si-BEA, SL-1, and ZSM-5 with a larger iodine (I₂) adsorption amount exhibit higher hydrophobicity than other zeolites. That is to say, the iodine (I₂) adsorption amount increases with hydrophobicity, suggesting that the adsorption of iodine (I₂) in the zeolite is due to hydrophobic bonding. The hydrophobicity is in the order of ZSM-5<SL-1<Si-BEA<SL-1F. Since the hydrophobicity of the zeolite increases with the Si/Al ratio, the zeolite according to the present invention capable of adsorbing iodine (I₂) has a Si/Al ratio (molar ratio) of 15 or greater, specifically 20 or greater, more specifically 30 or greater. For SL-1, SL-1F, and Si-BEA, which are free from Al, the Si/Al ratio is infinite (∞).

Meanwhile, using an apparatus for desorbing I₂by increasing temperature while injecting nitrogen gas as shown in FIG. 5, the degree of iodine desorption depending on temperature was investigated for activated carbon (AC) and the various zeolites Si-BEA, SL-1F, and SL-1 (FIG. 6). Although I₂is highly volatile, it is not desorbed easily even at high temperatures once it is adsorbed to the zeolite. As seen from FIG. 6, I₂was desorbed at 175° C. for the zeolites Si-BEA, SL-1F, and SL-1, unlike activated carbon (AC). That is to say, I₂is desorbed from all of these adsorbents when hot air or hot nitrogen above a certain temperature is injected. For activated carbon (AC), some of the adsorbed I₂that turned to I⁻ remained and iodine was not completely desorbed.

The XRD patterns of SL-1 powder (freshly calcined), SL-1 with 0.1%, 1.0%, 6.9%, 22.3% or 34.4% I₂adsorbed, and I₂-adsorbed SL-1 which has been recalcined (recalcination) were investigated. As seen from FIG. 7, it was observed that the peaks related to porosity disappeared when the nanowire channel in SL-1 was completely filled with I₂(34.4%). In addition, it can be seen from the XRD patterns shown in FIG. 7 that the porosity-related peaks appeared again for the I₂-adsorbed SL-1 which had been recalcined (recalcination), as in the fresh SL-1. This confirms that the backbone structure is maintained regardless of the adsorption and desorption of I₂.

Meanwhile, the amount (wt %) of iodide ion (I⁻) formed inside the solid adsorbent and in a solution with time was measured for activated carbon (AC) and the various zeolites SL-1F, Si-BEA, SL-1, ZSM-5, AgMOR, SBA-15, NaY, MOR, NaX, NaA, and CaA. The results are shown in FIG. 8a and FIG. 8b , respectively. FIG. 8a shows the amount (wt %) of iodide ion (I⁻) formed inside the solid adsorbent, FIG. 8b shows the amount (wt %) of iodide ion (I⁻) formed in a solution, and FIG. 8c shows the total amount of the formed iodide ion (I⁻).

As seen from FIGS. 8a-8c , the amount of iodide ion (I⁻) formed inside the solid adsorbent was the highest for activated carbon (AC). The amount of iodide ion (I⁻) formed in solutions was in the order of NaX>NaA>CaA>NaY. For MOR, AgM, ZSM-5, SL-1F, SL-1, Si-BEA, and SBA-15, iodide ion (I⁻) was hardly formed either inside the solid adsorbent or in the solution.

FIG. 9 shows the relationship between the Sanderson partial charge on oxygen and the total amount (wt %) of iodide ion (I⁻) formed inside the solid adsorbent and in the solution for activated carbon (AC) and the various zeolites SL-1F, Si-BEA, SL-1, ZSM-5, AgMOR, SBA-15, NaY, MOR, NaX, NaA and CaA.

From FIG. 9, it can be seen that the formation amount (wt %) of iodide ion (I⁻) is proportional to the Sanderson partial charge on oxygen for activated carbon (AC) and the various zeolites. Accordingly, the zeolite used as an iodine (I₂) adsorbent for preventing iodide ion (I⁻) formation may have a Sanderson partial charge on oxygen (−δ⁰) of specifically 0.2 or lower, more specifically 0.1-0.2.

As seen from FIGS. 1-9, the zeolites SL-1F, Si-BEA, SL-1, and ZSM-5 are advantageous in that they exhibit a high iodine (I₂) adsorption amount and hardly show iodide ion (I⁻) formation inside the solid adsorbent and in the solution. The zeolites SL-1F, Si-BEA, SL-1, and ZSM-5 have stronger hydrophobicity and a lower Sanderson partial charge on oxygen as compared to other zeolites.

Accordingly, the present invention is characterized in that a zeolite having a Si/Al ratio of 15 or greater is used as a zeolite for adsorbing iodine (I₂) and, among such zeolites, a zeolite having a Sanderson partial charge on oxygen (−δ⁰) of 0.2 or lower is used to prevent formation of iodide ion (I⁻) from the adsorbed I₂.

FIG. 10A shows the I₂-saturated adsorption amount (wt %) of activated carbon (AC) and the various zeolites Si-BEA, SL-1F, and SL-1 under different I⁻ concentrations. It can be seen that the zeolite according to the present invention can adsorb I₂even when it is dissolved in water as I⁻.

Additionally, FIG. 10B shows the I₂-saturated adsorption amount (wt %) of activated carbon (AC) and the various zeolites Si-BEA, SL-1F, and SL-1 in artificial seawater (ASW). It can be seen that the zeolite according to the present invention can adsorb I₂even when it is dissolved in seawater.

I₂is more soluble in seawater because it forms a complex. The zeolite according to the present invention can readily remove I₂, particularly radioactive I₂, when it is dissolved in seawater, underground water, etc.

Meanwhile, the zeolites of the present invention can also adsorb Br₂in water (FIG. 11).

The zeolite according to the present invention can adsorb I₂having not only stable I-127 but also all the isotopes of I described in Table 2.

TABLE 2

		Decay		Main γ-X-ray energy (keV)
Isotope	Half-life	mode	E_max(keV)	(abundance)

¹²³I

13.27

h

EC + β⁺

1074.9

(97%, EC)

159 (83%)

¹²⁴I	4.18	d	EC + β⁺	2557 (25%, EC), 3160	602.7 (63%), 723 (10%),
				(24%, EC), 1535 (12%, β⁺),	1691 (11%)
				2138 (11%, β⁺)

¹²⁵I	59.41	d	EC	150.6	(100%)	35.5 (6.68%), 27.2 (40%),
						27.5 (76%)

¹²⁶I	13.11	d	EC + β⁺, β⁻	869.4 (32%, β⁻), 1489 (29%,	338.6 (34%), 666.3 (33%)
				EC), 2155 (23%, EC)

¹²⁷I

Stable

¹²⁸I	24.99	m	β⁻, EC + β⁺	2119	(80%, β⁻)	442.9 (17%)
¹²⁹I	1.57 × 10⁷	y	β⁻	154.4	(100%)	39.6 (7.5%), 29.5 (20%),
						29.8 (38%)

¹³⁰I	12.36	h	β⁻	587 (47%), 1005 (48%)	536 (99%), 668.5 (96%),
					739.5 (82%)

¹³¹I

8.02

d

β⁻

606

(90%)

364.5 (82%)

¹³²I	2.30	h	β⁻	738 (13%), 1182 (19%),	667.7 (99%), 772.6 (76%)
				2136 (19%)

^132mI	1.39	h	IT, β⁻	1483	(8.6%, β⁻)	600 (14%), 173.7 (8.8%)
¹³³I	20.8	h	β⁻	1240	(83%)	529.9 (87%)
¹³⁴I	52.5	m	β⁻	1307	(30%)	847 (95%), 884 (65%)

¹³⁵I	6.57	h	β⁻	970 (22%), 1388 (24%)	1260 (29%)

Half-lives of the isotopes are given as m: minutes; h: hours; d: days; and y: years.
The decay mode: EC for electron capture; β⁺ for positron emission; β⁻ for beta emission; IT for internal transfer. An isotope may decay by more than one mode.

Meanwhile, the solubility (wt %) of iodine (I₂) of SL-1F and BEA was compared in various organic solvents. The results are shown in Table 3. Electron donor solvents can dissolve a large amount of I₂because they form electron donor-acceptor complexes. Even though silicalite-1 (SL-1F) is a weak electron donor, the solvent can dissolve a very large amount of I₂.

TABLE 3

	Solubility of I₂at	Solvent density	Solvent weight	Concentration
Solvent
	25° C. (g/100 mL)	(g/mL)	(g)	(%)	wt %

Ethanol	21.43	0.79	79.0	21.34	27.12
Diethyl ether	25.20	0.71	71.0	26.19	35.49
AcOH	14.09	1.05	105.0	11.83	13.42
Benzene	14.09	0.88	88.0	13.80	16.01
CHCl₃	14.09	1.48	148.3	8.68	9.50
CCl₄	2.603^a	1.59	159.0	1.61	1.64
Carbon disulfide (CS₂)	16.47	1.26	126.0	11.56	13.07
Water	0.029^b,	1.00	100.0	0.029,	0.029,
	0.078^c			0.078	0.078
Hexane (exp.	0.94	0.66	65.9	1.41	1.43
data)
Silicalite-1	63.72	1.80	180.0(100 mL)	26.14	35.40
(SL-1F)
BEA	56.96	1.61	161.0(100 mL)	26.25	35.60
AC	11.55	0.32	32.0(100 mL)	26.52	36.10

^aat 35° C.,
^bat 20° C.,
^cat 50° C., density of I₂= 4.93 g/mL.

As can be seen from Table 3, although the I₂adsorbed to the zeolite according to the present invention cannot be removed in water, it can be removed using organic solvents exhibiting high solubility for I₂. However, the I₂adsorbed to activated carbon (AC) cannot be removed even when organic solvents exhibiting high solubility for I₂are used. Since the zeolite according to the present invention is hydrophobic, it has a strong tendency to absorb the organic solvent and the absorbed organic solvent dissolves I₂, thereby releasing I₂from the zeolite.

The zeolite according to the present invention can be recycled indefinitely since the I₂adsorbed thereto can be completely removed using organic solvents such as ethanol. In contrast, activated carbon (AC) must be discarded after 3-4 uses because the I₂adsorbed thereto cannot be removed by water or organic solvents. Accordingly, whereas the zeolite according to the present invention can be used indefinitely when filled into a fixed-bed column since I₂adsorbed thereto can be completely removed using organic solvents, the activated carbon (AC) being filled into a fixed-bed column as an I₂adsorbent requires routine replacement.

Non-limiting examples of the organic solvent for dissolving I₂from the zeolite may include ethanol, diethyl ether, AcOH, benzene, CHCl₃, carbon disulfide or a mixture thereof.

Meanwhile, the I₂recovered from the zeolite and remaining dissolved in the organic solvent may be converted to small-sized AgI or AgIO precipitates by reacting with a AgNO₃aqueous solution for permanent burial.

The inventors of the present invention found that an iodine- or bromine-containing zeolite composite including a porous zeolite and iodine (I₂) or bromine (Br₂) confined in the pores of the zeolite exhibits semiconductor properties with a narrow band gap energy (E_g). For example, it may have a band gap energy E_g<3.0 eV and an electrical conductivity of 0.1 siemens/m or greater.

Specifically, a result of measuring the electrical conductivity of iodine-containing silicalite-1 (I₂@SL-1) by electron force microscopy was as follows:
σ_aalong a-axis=1.67×10⁴Sm⁻¹
σ_balong b-axis=1.99×10⁴Sm⁻¹

In addition, since the iodine (I₂) captured in the iodine-containing zeolite composite according to the present invention is not evaporated at temperatures of 50° C. or lower, it allows accurate quantification of iodine. It can be applied for a variety of chemical reactions requiring iodine because an accurate known amount of iodine is released by an organic solvent if the iodine-containing zeolite composite which has been quantitated is added to a reactor.

Additionally, the iodine-containing zeolite composite according to the present invention may be used as a controlled-release system by slowly adding a solvent that enables release of iodine.

This application also holds true for the bromine-containing zeolite composite.

Claims

What is claimed is:

1. A method of adsorbing I₂or Br₂and converting neither the adsorbed I₂to I⁻ nor the adsorbed Br₂to Br⁻, comprising

adsorbing I₂or Br₂on a I₂or Br₂adsorbent containing a zeolite having a Si/Al ratio of 15 or greater and a Sanderson partial negative charge on oxygen (−δº) of 0.2 or lower, wherein the zeolite is selected from the group consisting of SL-1F, Si-BEA and SL-1.

2. The method of claim 1, wherein the adsorbed iodine (I₂) comprises radioactive iodine.

3. A method of removing I₂or Br₂, comprising:

adsorbing I₂or Br₂without converting the adsorbed I₂to I⁻ or the adsorbed Br₂to Br⁻, on a I₂or Br₂adsorbent containing a zeolite having a Si/Al ratio of 15 or greater and a Sanderson partial negative charge on oxygen (−δº) of 0.2 or lower, wherein the zeolite is selected from the group consisting of SL-1F, Si-BEA and SL-1;

desorbing the adsorbed I₂or Br₂from the zeolite by contacting the I₂or Br₂adsorbent with an organic solvent dissolving I₂or Br₂, by heating the I₂or Br₂adsorbent, or by blowing the I₂or Br₂adsorbent in heated air or heated nitrogen; and

forming a precipitate by reacting the desorbed I₂or Br₂with AgNO₃.

4. The method for removing I₂or Br₂according to claim 3, wherein the organic solvent is ethanol, diethyl ether, AcOH, benzene, CHCl₃, carbon disulfide, or a mixture thereof.